Aromatic polyester resins have long been known. For instance, p-hydroxy benzoic acid homopolymer and copolymers have been provided in the past and are commercially available. Those aromatic polyesters normally encountered in the prior art have tended to be somewhat intractable in nature and to present substantial difficulties if one attempts to melt process the same while employing conventional melt processing procedures. Such polymers commonly are crystalline in nature, relatively high melting or possess a decomposition temperature which is below the melting point, and when molten frequently exhibit an isotropic melt phase. Molding techniques such as compression molding or sintering may be utilized with such materials; however, injection molding, melt spinning, etc., commonly have not been viable alternatives or when attempted commonly have been accomplished with difficulty. Such polymers commonly cannot be melt extruded to form nondegraded fibers. Even those aromatic polymers which exhibit a melting point below their decomposition temperature commonly melt at such high temperatures that quality fibers may not be melt spun. For instance, fibers melt extruded at extremely high temperatures commonly possess a voidy internal structure and diminished tensile properties.
Representative publications which discuss aromatic polyesters include: (a) Polyesters of Hydroxybenzoic Acids, by Russell Gilkey and John R. Caldwell, J. of Applied Polymer Sci., Vol. II, Pages 198 to 202 (1959), (b) Polyarylates (Polyesters from Aromatic Dicarboxylic Acids and Bisphenols), by G. Bier, Polymer, Vol. 15, Pages 527 to 535 (August 1974), (c) Aromatic Polyester Plastics, by S. G. Cottis, Modern Plastics, Pages 62 to 63 (July 1975), and (d) Poly (p-Oxybenzoyl Systems): Homopolymer for Coatings: Copolymers for Compression and Injection Molding, by Roger S. Storm and Steve G. Cottis, Coatings Plast. Preprint, Vol. 34, No. 1, Pages 194 to 197 (April 1974). See also, U.S. Pat. Nos. 3,039,994; 3,169,121; 3,321,437; 3,553,167; 3,637,595; 3,651,014; 3,723,388; 3,759,870; 3,767,621; 3,778,410; 3,787,370; 3,790,528; 3,829,406; 3,890,256; and 3,975,487.
Also, it more recently has been disclosed that certain polyesters may be formed which exhibit melt anisotrophy. See for instance, (a) Polyester X7G-A Self Reinforced Thermoplastic, by W. J. Jackson, Jr., H. F. Kuhfuss, and T. F. Gray, Jr., 30th Anniversary Technical Conference, 1975 Reinforced Plastics/Composites Institute, The Society of the Plastics Industry, Inc., Section 17-D, Pages 1 to 4, (b) Belgian Pat. Nos. 828,935 and 828,936, (c) Dutch No. 7505551, (d) West German Nos. 2520819, 2520820, 2834535, 2834536, and 2834537, (e) Japanese Nos. 43-233, 2132-116, 3017-692, and 3021-293, (f) U.K. Patent Application No. 2,002,404, and (g) U.S. Pat. Nos, 3,991,013; 3,991,014; 4,066,620; 4,067,852; 4,075,262; 4,083,829; 4,118,372; 4,130,545; 4,153,779; 4,156,070; 4,159,365; 4,161,470; and 4,169,933. See also commonly assigned U.S. Ser. No. 877,917 filed Feb. 15, 1978 (now U.S. Pat. No. 4,184,996); Ser. No., 010,392, filed Feb. 8, 1979 (now U.S. Pat. No. 4,238,599); Ser. No. 10,393, filed Feb. 8, 1979 (now U.S. Pat. No. 4,238,598); Ser. No. 17,007, filed Mar. 2, 1979 (now U.S. Pat. No. 4,230,817); Ser. No. 021,050, filed Mar. 16, 1979 (now U.S. Pat. No. 4,224,433); Ser. No. 032,086, filed Apr. 23, 1979 (now U.S. Pat. No. 4,219,461); and Ser. No. 054,049, filed July 2, 1979 (now U.S. Pat. No. 4,256,624).
Commonly assigned U.S. Pat. No. 4,083,829 discloses inter alia a melt processable polyester of parahydroxy benzoic acid, 2,6-naphthalene dicarboxylic acid, isophthalic acid, and unsubstituted hydroquinone. It has been found during subsequent testing that such polyester when subjected to certain extreme environments is susceptible to hydrolytic degradation to a significant degree as discussed hereafter. For instance, if the polyester is in the form of a fiber and is subjected to such environments, the fiber strength is significantly reduced upon the passage of time. U.S. Pat. No. 4,169,933 discloses a polyester of parahydroxy benzoic acid, 2,6-naphthalene dicarboxylic acid, terephthalic acid, and hydroquinone.
It is an object of the present invention to provide an improved melt processable polyester which exhibits an anisotropic melt phase.
It is an object of the present invention to provide a novel melt processable polyester which exhibits a substantially greater hydrolytic stability than the polyester of U.S. Pat. No. 4,083,829.
It is an object of the present invention to provide an improved polyester which is suited for the formation with ease of quality melt extruded fibers, molded articles, and melt extruded films.
It is an object of the present invention to provide an improved melt processable polyester capable of forming an anisotropic melt phase at a temperature below approximately 320.degree. C., preferably below approximately 300.degree. C., and most preferably below approximately 290.degree. C.
It is an object of the present invention to provide a novel polyester which is capable of melt processing in standard equipment commonly utilized with polyethylene terephthalate.
It is an object of the present invention to provide an improved polyester which forms an anisotropic melt phase at a temperature well below its decomposition temperature and which may form quality high performance fibers.
It is an object of the present invention to provide improved polyester fibers which particularly are suited for use as fibrous reinforcement in a rubber matrix, or in other matrices (e.g., polyester, polyepoxide, etc.) which are subjected to extreme conditions of heat and moisture during their operating lives.
These and other objects, as well as the scope, nature and utilization of the invention will be apparent to those skilled in the art from the following detailed description.